Command /Developer/usr/bin/clang failed with exit code 1
You can also get this error of you accidentally include the implementation file rather than the header file. e.g. #import "MyClass.m" instead of #import "MyClass.h"
This is the reason ld: duplicate symbol _addScore
In your project you have _addScore file more than one time. check your project hierarchy.
After receiving the exact same error, I noticed that I somehow had gotten two .h files with the same name in my project. Deleting the duplicate from the project's folder (not just removing the reference) solved the issue for me.